1. Field of the Invention
The present invention generally relates to variable inductors, and more particularly, to a variable inductor for use in mobile communication devices.
2. Description of the Related Art
Electronic devices that are desired to be compact, in particular, mobile communication devices such as cellular telephones and automobile telephones, require compact components incorporated therein. Furthermore, as the frequency of operation of a device increases, the circuit becomes more complicated, and narrow variation and strict tolerance are required for the components incorporated therein. In effect, however, each component has the variation, and a circuit on which such components are merely mounted may not be correctly operated. In order to avoid such problems, methods have been conceived in which variable components are used for some of the components constituting the circuit, such that the variable components are finely adjusted to correctly operate the circuit. One method is to use variable inductors and one such conventional inductor has an inductance adjustment portion (trimming pattern portion).
FIG. 8 is a perspective view of an exemplary variable inductor 1 having an inductance adjustment portion. The variable inductor 1 includes a spiral coil 3 disposed on the surface of an insulating substrate 2. The inductance adjustment portion includes a plurality of trimming electrodes 4 which are arranged in a ladder configuration, and is located in a region defined by the coil 3. One end 3a of the coil 3 is electrically connected to an external electrode 7, and the other end 3b extends across an insulator film 5 and is electrically connected to an external electrode 8. The trimming electrodes 4 are sequentially trimmed one-by-one by irradiating a laser beam from above the variable inductor 1, so that the inductance between the external electrode 7 and the external electrode 8 may be finely adjusted in a stepwise manner.
FIG. 9 is a perspective view of another conventional variable inductor 11. The inductor 11 includes a spiral coil 13 disposed on the surface of an insulating substrate 12. An inductance adjustment portion includes trimming electrodes 14a to 14d, and the trimming electrodes 14a to 14d are extended halfway from the coil 13 to the outside of a region defined by the coil 13. The trimming electrodes 14c and 14d are located on insulator films 15a and 15b , respectively. One end 13a of the coil 13 is electrically connected to an external electrode 17, and the other end 13b extends across an insulator film 15c and is electrically connected to an external electrode 18. The trimming electrodes 14a to 14d are sequentially trimmed one-by-one so that the inductance between the external electrode 17 and the external electrode 18 may be adjusted.
However, the variable inductor 1 shown in FIG. 8 has a small area where the inductance adjustment portion is disposed, thus providing a small variable range for the inductance, making it difficult to acquire a variable inductance range required for a circuit adjustment. This is because increasing the area where the inductance adjustment portion is disposed in order to obtain a required variable range prevents compactness of the inductor. Furthermore, the variable inductor 1 is designed so that the electrodes 4 are arranged in a region defined by the coil 3, and the electrodes 4 become obstacles to a magnetic field generated by the coil 3. As a result, a problem occurs that the Q factor of the inductor 1 is reduced.
In the variable inductor 11 shown in FIG. 9, on the other hand, the inductance is adjusted per turn, and the inductance is not finely adjusted. Hence, even if the variable inductor includes the optimum inductance for a circuit adjustment within the variable range thereof, there was a case where the optimum value could not be obtained. In addition, the variable inductor 11 makes it difficult to connect the trimming electrodes 14a to 14d at a substantially uniform interval of coil length, resulting in difficulty in accurately adjusting the inductance in a stepwise manner by a substantially constant value. Furthermore, since the trimming electrodes 14a to 14d are not arranged in a row in the trimming order, the trimming operation is cumbersome and is not suitable for mass production.
In order to overcome the problems described above, preferred embodiments of the present invention provide a variable inductor having a high Q factor and a wide variable range of inductance which can be finely adjusted with ease.
To this end, according to a preferred embodiment of the present invention, a variable inductor includes an input external electrode and an output external electrode, a coil defined by electrically connecting at least two spiral coil pattern portions in series between the input external electrode and the output external electrode, at least one trimming electrode provided in each of the at least two spiral coil pattern portions, each trimming electrode having one end connected to the spiral coil pattern portion, and a lead out electrode connected to the other end of each trimming electrode, wherein the lead out electrode is connected to one of the input external electrode and the output external electrode.
Preferably, the trimming electrodes are arranged in a row and are connected to the spiral coil pattern portions, such that the trimming electrodes are sequentially cut starting from a trimming electrode at an end, whereby the inductance of the coil is increased accordingly.
Accordingly, at least two spiral coil pattern portions are electrically connected in series between the input external electrode and the output external electrode to define a coil, where the trimming electrodes may be arranged in the trimming order. This facilitates the trimming operation, and avoids such an inconvenience as erroneous cutting during the trimming, thereby providing more reliable trimming. This further allows for a wider variable inductance range required for a circuit adjustment. The trimming electrodes are sequentially trimmed (cut) one-by-one so that the inductance of the coil may be finely adjusted in a stepwise manner by a constant value.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments with reference to the attached drawings.